Tennant made his debut as the Tenth Doctor in June 2005, and last filled the role on January 1, 2010. Since exiting Who, he has appeared in the miniseries Single Father, The Escape Artist and Spies of Warsaw (premiering April 3).

Piper played companion Rose Tyler starting in May 2005, and exited the series with Tennant in his final episode, “The End of Time.” She went on to headline the series Secret Diary of a Call Girl for four seasons.

Also as part of the 50th anniversary plans, BBCA is co-producing a TV-movie chronicling the series’ genesis and the Time Lord’s maiden voyage on Nov. 23, 1963. An Adventure in Space and Time will star David Bradley (aka the Harry Potter films’ Argus Filch) as William Hartnell, the series’ first Doctor.

Which other Doctor Who alumni do you hope sign on for the anniversary celebration?